The present invention relates to a radio receiver. More particularly, the invention relates to an electronic tuning control circuit of a radio receiver utilizing a voltage memory element.
In general, the tuning circuit of a radio receiver may consist of a mechanical type tuning system or an electronic tuning system. In the conventional electronic tuning system, a sawtooth wave is applied from a sawtooth wave generator to a variable reactance element, or, more particularly, to a variable capacitance diode forming the tuning circuit, for sweeping the tuning frequency. When the tuning frequency tunes to the selected broadcasting frequency, the frequency sweep stops. However, in such a conventional electronic auto-tuning system, there has always been the disadvantage that it is impossible to maintain the voltage at the tuning period for the variable capacitance element for a long time. This is due to the fact that the leak discharge from the capacitor forming the sawtooth wave generator cannot be blocked. As a result, for example, when the power switch is turned OFF once, and then turned ON again, or when the broadcasting signal is once suspended or becomes weak, the previous broadcasting signal cannot be received. The disadvantage results in troublesome operation when the radio receiver is a mobile installation.
The principal object of the invention is to provide a radio receiver of high performance which stably maintains the receiving condition.
An object of the invention is to provide an electronic auto-tuning control circuit which stably maintains the control voltage to the variable reactance element forming the tuning circuit, for a long time.
Another object of the invention is to provide a radio receiver which excels in operability when it is in a mobile installation.
Still another object of the invention is to provide a tuning control circuit of simple structure, which is inexpensive in manufacture and functions efficiently, effectively and reliably to automatically tune a radio receiver.
Yet another object of the invention is to provide a tuning control circuit having a voltage memory element for automatically tuning a radio receiver.